The interesting thing is that things used to work up until today. I had absolutely no issues with lighttpd beforehand.
I simply followed this guide, and installed pihole by using
curl -L https://install.pi-hole.net | bash
Repairing pihole does not work:
root@Alexandria:~# pihole -r
[✓] Root user check
[i] Existing PHP installation detected : PHP version 5.6.40-0+deb8u9
[i] Repair option selected
[✗] Disk space check
[i] Unknown free disk space!
We were unable to determine available free disk space on this system.
You may override this check, however, it is not recommended.
The option '--i_do_not_follow_recommendations' can override this.
e.g: curl -L https://install.pi-hole.net | bash /dev/stdin <option>